Aggression and social experience in domesticated rats.

Small colonies of rats were established, using adult animals that had either received continuous social experience or had been isolated since weaning. Unfamiliar "intruder" rats--with or without postweaning social experience--were exposed individually to the colonies for a 21-hr. period. Behavioral observations and an assessment of the intruder's physical condition indicated that serious fighting, physical injuries, and large weight losses occurred only when an isolation-reared intruder was placed into a colony of socially experienced rats. These results demonstrate that aggression is a joint function of the rearing history of both the colony and the intruder and that social experience plays an important role in the behavioral development of this species.